Polyimide/Ionic Liquid Composite Membranes for Middle and High Temperature Fuel Cell Application: Water Sorption Behavior and Proton Conductivity

• Main Authors: Kateryna Fatyeyeva, Sergiy Rogalsky, Stanislav Makhno, Oksana Tarasyuk, Jorge Arturo Soto Puente, Stéphane Marais
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Membranes
• Subjects: porous polyimide membrane; ionic liquid; conductivity; vapour sorption; thermal stability
• Online Access: https://www.mdpi.com/2077-0375/10/5/82

Four water insoluble room-temperature protic ionic liquids (PILs) based on the <i>N</i>-alkylimidazolium cation with the alkyl chain length from 1 to 4 and bis(trifluoromethylsulfonyl)imide anion were synthesized and their chemical structure was confirmed by the ¹H NMR and ¹⁹F NMR analysis. PILs were revealed to be thermally stable up to 360 and 400 °C. At the same time, the proton conductivity of PILs was found to be dependent mostly on the temperature and, to a less extent, on the type of the cation, i.e., the increase of the conductivity from ~3 × 10⁻⁴ S/cm at 25 °C to 2 × 10⁻² S/cm at 150 °C was observed. The water vapour sorption capacity of PILs was evaluated as a function of relative humidity and the influence of the alkyl chain length on the phase behaviour in the PIL-water system was discussed. The composite polyimide/PILs membranes were prepared by the PIL immobilization in the porous polymer (Matrimid^® 5218) film. The composite membranes showed a high level of proton conductivity (~10⁻³ S/cm) at elevated temperatures (up to 160 °C). The obtained results reveal that the elaborated composite polyimide/PIL membranes are promising candidates for the application as proton exchange membrane at middle and high temperatures.